Mitigation of the multipath effect in BDS-based time transfer using a wave-absorbing shield

The pseudorange multipath effect is a major unmodeled error source in Global Navigation Satellite System (GNSS) time transfer. It is critical to mitigate the pseudorange multipath effect in GNSS time transfer. To reduce such a multipath effect, we employ a technique of installing a wave-absorbing shield on GNSS stations. In this contribution, extensive evaluations were conducted with BeiDou Navigation Satellite System (BDS) datasets collected from the KUN1 and SHA1 stations of the international GNSS Monitoring and Assessment System (iGMAS) network in an eight-month period from January 1 to September 1, 2016. Comparative analysis demonstrated that the pseudorange multipath effect was reduced by 29.9-38.9% on all available frequencies of BDS. The solutions of BDS common-view (CV), all in view (AV), and precise point positioning (PPP) in a 31-day period were presented before and after the wave absorbing installation, respectively. After applying the wave-absorbing shield, the uncertainty improvement of BDS PPP time transfer was by 22.86, 21.48, 11.72, and 15.00% for the constellation combinations of GEO + IGSO + MEO, GEO + IGSO, GEO + MEO, and IGSO + MEO, respectively. Meanwhile, the uncertainty of CV time transfer was improved by 15.48, 24.18, 17.84, 29.69, and 15.26% for the constellation combinations of GEO + IGSO + MEO, GEO, IGSO, MEO and IGSO + MEO and 12.62, 20.94, 9.39, 29.02, and 14.38% for AV time transfer, respectively. Furthermore, the frequency and time stability were improved to varying degrees with the wave-absorbing shield installation. The results demonstrated that the type A uncertainty of BDS time transfer can be improved significantly by installing the wave-absorbing shield. Hence, it provides a good choice for high-precision GNSS time and frequency transfer with multipath mitigation by installing the wave-absorbing shield. (C) 2018 COSPAR. Published by Elsevier Ltd. All rights reserved.